Arecord->FFMPEG works but FFMPEG w/ ALSA stutters?

Question

I am trying to stream audio from my Pi Zero and my I2s MEMS mic. I would like to stream using FFMPEG and ALSA (which I have already compiled) but I'm running into stuttering issues.

1. FFMPEG + ALSA

   ~/special/ffmpeg/ffmpeg -report -f alsa -ar 48000 -ac 2 -acodec pcm_s32le -i mic_sv -f lavfi -i testsrc -c:v h264_omx -c:a aac -ab 32k -bufsize 32k -f flv rtmp://209.85.230.23/live2/KEY

This results in constant stuttering and choppiness.

2. Arecord piped directly to FFMPEG

   arecord -Dmic_sv -c2 -r48000 -fS32_LE | ~/special/ffmpeg/ffmpeg -report -acodec pcm_s32le -i - -f lavfi -i testsrc -c:v h264_omx -acodec aac -ab 32k -bufsize 32k -f flv rtmp://209.85.230.23/live2/KEY

This results in a coherent audio stream, but with skipping every 5 seconds or so.

3. Arecord recorded to a wav file, piped into FFMPEG

   arecord -Dmic_sv -c2 -r48000 -fS32_LE -twav temp.v & ~/special/ffmpeg/ffmpeg -report -re -i temp.v -f lavfi -i testsrc -c:v h264_omx -ac 2 -acodec aac -ab 32k -bufsize 32k -async 2 -f flv rtmp://209.85.230.23/live2/KEY

This results in a perfect audio stream.

I don't know why #3 works but #2 and #1 cause problems. Any suggestions?

Answer 1

Well well off we go to my every first Stackoverflow post :)

So you probably experience a message saying [alsa buffer run] or similar. The reason for this is indeed because the buffer fills up faster than it can be processed. The only real mitigation I found was to change the sampling rate to 22050hz

here is some code that should work:

ffmpeg -re -v verbose -hide_banner  -f v4l2 -thread_queue_size 1024 -re -i temp.v  -ar 11025 -f alsa -ac 1 -thread_queue_size 1024 -i default  -b:a 64k  -c:v libx264  -preset ultrafast -strict experimental -f flv -g 20 -keyint_min 20 -maxrate 2M -bufsize 6M -acodec aac  rtmp://209.85.230.23/live2/KEY 

p.s. Sorry for the late reply.